Most conventional combing rollers are formed by a cylindrical body having a spiral circumferential groove located on an outer circumference of the cylindrical body. Saw-like teeth are mounted in the groove and perform a sliver singling-out operation.
At high rotational speeds required in conventional open end spinning machines, such combing rollers are unsatisfactory because the rollers have a relatively short service life. A subsequent surface treatment of the combing roller accentuates the problems caused by rolling as well as those of the saw-like teeth surface, which problems substantially hinder the combing roller function. Another drawback of such combing rollers is the tendency for impurities and fiber clusters to stick to the grooves formed between the tooth-free sections of the saw-like surface near the circumference of the cylindrical body which produces irregularities and other faults in the yarn being spun. An advantageous feature of such a conventional combing roller is that the teeth are formed on the surface in a spiral so that the number of teeth actually in engagement with a fiber sliver varies over time.
There are known combing rollers, e.g., as described in DE OS 19 39 683, in which saw-like teeth are formed on the surface of a cylindrical body by forming a spiral groove with axially oriented notches intersecting a groove upper part so as to create tooth front and back faces.
In an improvement described in DE 38 27 344, a combing roller includes a ring-like body having teeth formed on an outer circumference by substantially axially oriented notches which cooperate with circumferentially oriented gaps, wherein the circumferentially oriented gaps are deeper than the notches located between the teeth.
Because of the last-mentioned feature, the operating part of such a combing roller is similar to the combing roller with the saw-like surface because such a roller produces irregularities in the yarn being spun and causes fibers to stick to the lower sections of the gaps between the tooth rows. The fibers are drawn to a root of each tooth and, when transported into a feeding channel, the loosening of the fibers from the surface of the combing roller is partially obstructed, thereby destroying the uniformity of the yarn being spun.
However, the main drawback of such a combing roller is the axially oriented notches forming the front and back faces of the teeth. Because of this arrangement, whole rows of teeth of the combing roller simultaneously contact the sliver creating sudden impact forces and jerking motions acting on the sliver. This results in the sliver not being fed smoothly and continuously but intermittently and with a jerking motion causing harmful effects on the yarn being spun.